Vane control for air classifier



April 29, 1969 F. J. MlKslTz 3,441,133

VANE CONTROL FOR AIR CLASSIFI'ER Filed May 4, 1966 l sheet of :5

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April 29, 1969 F. J. MlKslTz VANE CONTROL FOR AIR CLASSIFIER SheerIFiled May 4, 1966 lvllllflllg,

u w, Wm lf VI United States Patent O 3,441 133 VANE CONTRGL FR AIRCLASSIFIER Frank J. Miksitz, Nazareth, Pa., assignor to Meuch and U.S.Cl. 209-139 5 Claims ABSTRACT F THE DISCLOSURE In an air classifier, animproved drive for the movable control vanes which are disposed in acircular pattern includes a mechanical transmission associated with eachvane and flexible drive shafts connecting the transmissions together sothat a single motor can be employed to adjust all the vanessimultaneously. Each transmission moves its respective vane in or out ofthe classifier by means of a chain drive which is so constructed as tominimize dust packing and freezing problems.

The particle size of the comminuted particles issuing from theclassifier is measured by withdrawing a portion of the stream with ascrew conveyor, delivering the solids to the top of a sample tube as auniformly loosely compacted mass, urging the solids in the form of anunagitated column through the tube with the aid of a plunger and chains,and measuring the density of the moving column with a gamma ray densitymeter.

This invention relates to centrifugal air classifiers for treating drycomminuted solids and in particular to the control of this type ofclassifier. It also relates to the continuous measurement of theparticle size of a stream of dry comminuted material and to the accuratemetering of dry comminuted material.

As is known, the term air classifier refers to a pneumatic device whichseparates a dry comminuted material into two or more fractions each moreclosely sized than the feed material. These devices are employed, forexample, to obtain from a finely ground material, such as cement or ore,a sized fraction and to return the coarser particles to the grindingequipment. It is often necessary to obtain a product of closely-controlled particle size, and to this end it is conventional toperiodically measure the particle size in the discharge stream of theclassifier and to make adjustments to the control features of the latterso as to increase or decrease the particle size being separated from thefeed. The present invention provides an improved mechanical drive forthe control devices commonly employed in one type of classifier and alsoprovides an improved testing ydevice for automatically measuring theparticle size in the classifier discharge or in other streams of drycomminuted material.

Referring more specifically to the feature of the invention whichrelates to the control of a classifier to obtain a desired grading ofparticle size, it will be understood that the type of classifier beingconsidered is in general use and that no detailed description of itsstructure and operation is required here. Briefiy, this type ofclassifier comprises inner and outer concentric cones having theirsmaller ends directed downwardly and terminating in separate dischargeopenings for coarse and fine particles. Comminuted feed solids to beclassified are fed downwardly into the top of the machine where they areacted on by a horizontal rotating -distributor plate and by air currentsgenerated by a horizontal fan. Control of particle size classificationis effected in part by the adjustment of the horizontal position of aplurality of plates or vanes disposed in a circumferential pattern inthe upper part of the machine so as to control the air currents.Typically, the vanes are mounted on threaded rods which project3,441,133 Patented Apr. 29, 1969 ice radially through the vertical sidewall of the machine and which are provided at their outer ends withrotatable adjusting nuts. Adjustment of the rods in their longitudinaldirection is obtained by rotating the nuts, this operation usually beingcarried out manually with hand tools. In practice the manual adjustmentof the nuts often becomes quite difficult as a result of the packing ofdust in the threads and consequent freezing or binding of the assembly.A further disadvantage of the arrangement is that considerable time isrequired to adjust all the nuts with the result that during this periodthe particle size in discharge stream does not correspond to the desiredsize.

According to the principles of one feature of the present inventionthere is provided an improved drive for the control vanes whichautomatically adjusts a plurality of vanes simultaneously and which isnot subject to freezing by packed dust. Briefly, the improved drivecomprises ya mechanical drive subassembly associated with each vane, asingle source of reversible rotary power associated with a plurality ofvanes and a transmission for delivering rotary power to all thesubassemblies simultaneously. In the ypreferred construction thetransmission includes a plurality of flexible drive shafts connectingthe subassemblies with each other, each flexible shaft lying in an arcon the circumferential pattern of the subassemblies. Each subassembly inthe preferred embodiment includes a longitudinally -movable control rodcarrying a vane at its inner end and a chain drive for convertingrotational movement into longitudinal movement of the rod, thearrangement being constructed to minimize dust packing and freezingproblems so that excessive stress will not be developed in thetransmission. This is highly important for automation of the equipment,because true automation exists only when substantially every likelihoodof breakdown has been eliminated.

Closely related to the automatic drive for the vanes in an airclassifier is a second feature of the present in- IVention which isconcerned with obtaining a rapid and substantially continuous analysisof the particle size in the discharge stream of the classifier. Thetechnique of measuring particle size which is in general use includesthe periodic withdrawal of a sample from the classifier discharge and alaboratory-type analysis of the sample. Generally the sample is testedwith a gas-permeability instrument which measures the resistance of apredetermined weight and predetermined volume of the sample to the flowof gas therethrough, the resistance being an indication of the particlesize when the instrument has been properly calibrated. The time lap-selbetween the taking of a sample and the determination of particle sizevaries with the particular instrument and the number of refinementswhich have been incorporated to speed up operation, but in any event,the analysis of the discharge stream by this means is at bestintermittent and involves delays which when coupled with the usualmanual adjustment of the vanes does not permit rapid adjustment of theclassifier vanes following a change in particle size.

According to the principles of the second feature of the presentinvention there is provided a particle size tester which may be operatedsubstantially continuously to give a signal substantiallyinstantaneously with the passage of classified material out of theclassifier so that immediate adjustment of the vanes may be effected assoon as a change in particle size is sensed. The tester makes use of aknown instrument, a density gauge of the nuclear radiation absorptiontype, in a heretofore unknown manner which permits the automaticmeasurement of the size of dry solids. More specifically, the testerincludes a special sampling device which is designed to pass a column ofcomminuted material past the detecting head of the density measuringinstrument at a constant rate and at a constant degree of compaction.Under these conditions the density of the material passing the detectoris constant for a given particle size of a given material. A change inparticle size results in a change in density and this in turn results ina change in the output signal of the instrument. The signal may beemployed to give visual instructions to an operator or it may be feddirectly into a control circuit for the vane dri-ve so as to effect afully automated system.

The sampling device constructed in accordance with the principles of thepresent invention includes a special plunger which cooperates with thebore of a vertical sample tube to assure that dry powdered solids in thetube will be metered at a carefully controlled rate. Briefly, theplunger is constructed in the form of a slightly flexible truncatedhollow cone the periphery of which at its larger end closely fits thebore of the tube. In a preferred construction the plunger is formed of atruncated thinwalled spring steel cone the larger end of which isdivided into a plurality of slightly arcuate segments by radial slots.The arcuate segments are slightly fiexible so as to form a good sealwhile at the same time compensating for variations in the bore of thetube.

While the tester is described hereinafter in combination with an airclassifier it will be understood that the tester is not limited to thiscombination and may be employed to test the particle size of any streamor mass of dry, powdered solids. It will be understood, also, that thespecial plunger construction has application wherever metering of drysolids is desired and may be employed, for example, to'dispense a firstpowder at a controlled rate into a stream of a second powder. Theinvention will be further understood from the following detaileddescription taken with the drawings in which:

FIGURE 1 is an elevational view of an air classifier having a vanecontrol and a particle size tester constructed according to theprinciples of the present invention;

FIGURE 2 is a fragmentary horiozntal sectional view of the airclassifier of FIGURE l taken above the level of the control vanes;

FIGURE 3 is a vertical sectional view of one of the drive subassembliesof FIGURE l;

FIGURE 4 is an end View, with some parts removed, of the drivesubassembly of FIGURE 3;

FIGURE 5 is a fragmentary elevational view, on an enlarged scale, of theparticle size tester of FIGURE l;

FIGURE 6 is a sectional view taken on the line 6-6 of FIGURE 5;

FIGURE 7 is a sectional View taken on the line 7-7 of FIGURE 5;

FIGURE 8 is a fragmentary vertical sectional View of the sample tube andplunger of FIGURE 5; and

FIGURE 9 is a fragmentary elevational view of the lower end of thesample tube.

Referring to FIGURE l there is shown an air classifier 10 of the kindwhich includes an inner cone member 12 and a concentric outer coneymember 14 both disposed below a cylindrical portion 16 havingassociated therewith a feed conduit 18 for the introduction of drycomminuted material. The inner cone 12 terminates at its lower end in aninclined discharge -pipe 20 for coarse solids. The outer cone 14terminates at its lower end in a vertical discharge section 22 for finesolids. Associated with the fine discharge section 22 is a sampling andtesting device 24 which includes an upper screw conveyor 26 forwithdrawing a portion of the fine solids and a lower conveyor 28 forsubsequently returning the withdrawn solids. The sampling and testingdevice 24 is described in more detail with reference to FIGURES 5-9.

The air classifier 10 is of a known internal construction and need notbe described in detail. This type of machine typically includes in theupper cylindrical portion a horizontal rotating plate (not shown), ahorizontal rotating fan (not shown) and a plurality, for examplesixteen, of horizontal vanes 30 (FIGURE 2) which are disposed in spacedapart relationship in a circular pattern. Powdered solids entering thetop of the machine are distributed in radial directions and are thenacted on by air currents created by the fan. Separation of coarseparticles from fine particles takes place by centrifugal force with thecoarse particles being collected in the inner cone 12 and the fineparticles being collected in the outer cone 14. The size of the fineparticles which are separated is controlled within limits by the size ofthe circular opening defined by the pattern of the vanes 30.Accordingly, the vanes 30 are adapted to be adjustable in radialdirections so that the size of the central opening may be adjusted. Asalready pointed out it is conventional to mount each vane 30 on aradially extending rod having a threaded outer end projecting throughthe side wall of the machine and to provide a rotatable adjusting nutfor each rod.

According to the principles of one feature of the present invention thevanes 30 are provided with a power driven adjusting system which movesall the vanes simultaneously and which is relatively free from bindingdue to the packing of dust into the drive mechanism. As pointed outheretofore power driven systems previously have not been consideredpractical because of the frequent necessity to free the bound-up drivemechanism. In the construction illustrated in FIGURES 1-4 each vane 30is provided with a powered adjusting assembly in the form of a specialtransmission 32 which converts rotary drive motion into longitudinalmovement of a vane control rod 34. As seen in FIGURES l and 2 thetransmissions 32 are Supported in spaced apart relationship along thecircumference of the cylindrical portion 16 of the classifier 10. Eachtransmission 32 includes an endless chain 40 looped over a pair ofsprocket wheels 42, 44 which are spaced apart along a radius of theclassifier 10. The inner sprocket wheel 42 is disposed within theclassifier 10 and the outer sprocket wheel 44 is disposed within ahousing 46 which is secured to the exterior of the classifier by boltsy48. The inner sprocket wheel 42 is fixed to a shaft 50 which isjournalled in a bracket 52 depending from the inner end of an elongatedsupport member 54. The outer end portion of the latter is slidablyretained between a pair of side walls 56 and a top wall 58 which formpart of the housing 46. The outer sprocket 44 is fixed to an input driveshaft 60 which is journalled in fiange bearings 62 mounted on the sidewalls 56 of the housing 46. The shafts 50 and 60 are parallel to eachother, and the input drive shaft 60 is disposed generally tangent to acircle drawn through the outer ends of all the transmissions 32.

The elongated support lmember 54 also supports the control rod 34 forthe respective vane 30. As shown in FIGURES 3 and 4 the member 54 is achannel-like member having its open side facing downwardly and definedby opposed flanges 64 which project toward the center line of thechannel. The control rod 34 is slidably retained in the bore of thechannel 54 by means of four radial ribs 65 and is connected to the upperrun of the chain 40 by a downwardly projecting member 66 which rides inthe slot between the fianges -64. The channel member 54 can be movedlongitudinally inwardly by means of an adjusting screw 72 carried by thehousing 46 for the purpose of adjusting the tension in the chain 40.Immediately below the adjusting screw 72 the outer wall of the housing46 is provided with a hole 73 through which the position of the rod 34may be measured manually. A fixed structure 74 forming part of theinternal arrangement of the classifier 10 supports the rod at a locationinwardly of the channel 54.

According to an important aspect of the present invention thetransmissions 32 are drivingly interconnected so as to be drivensimultaneously when it is desired to adjust the classifying action ofthe machine 10. To this end a single source of driving power isdrivingly connected to a plurality of the transmissions 32, preferablyby means of fiexible drive shafts. As shown, the driving power sourceincludes a reversible gear motor 76 and a speed reducer 78, the latterhaving a double-ended output shaft 80 disposed between two of thetransmissions 32 and lying generally tangent tothe aforementioned circledrawn through the outer ends of the transmissions 32. The ends of theoutput shaft 80 are connected to the nearest ends of the input shafts 60of the two adjacent trans missions 32 by means of two flexible driveshafts 82. All the other transmission input shafts 60 are interconnectedin series with the first-mentioned input shafts by a plurality offlexible drive shafts 84. As seen in FIGURE 2 when these connections aremade, all the flexible shafts 84 will lie generally on theaforementioned circle.

The illustrated embodiment of the drive arrangement includes, asrefinements, a clutch 86 and a handwheel 88 disposed between the gearmotor 76 and the speed reducer 78. Conveniently, a tachometer 90 mayalso be provided for indicating the position of the vanes. To preventdamage to the drive or to the transmissions 32one of the transmissions32 may be provided with a limit switch 92 which is electricallyconnected to the motor 76. As shown in FIGURE 4 the switch 92 is mountedon the housing 46 and is actuated by a rod 94 connected at its inner endto the chain 40.

The flexible drive shafts 84 are of conventional construction. As isknown, shafts of this type are formed from a single straight wire corearound which is wound a plurality of layers of high tensile strengthwire, successive layers being wound with alternating pitch directions.The result is a exible cable-like structure which is capable oftransmitting rotary motion through a curved path in either directionwith little or no lag between the drive element and the driven element.Conventionally the shafts are manufactured with attached end fittings,such as coupling members 96 shown in FIGURE 4.

Reference is now made to that part of the invention which relates to theprovision of a signal which is a measure of the particle size of thecomminuted solids and which may be employed for various purposesincluding the control of the direction and period of operation of thevane control motor 76. Heretofore, in the operation of air classifiers,it has been the practice to take samples of the product periodically,measure the particle size in each sample independently and make periodicadjustments on the basis of the measurements. The present inventioncontemplates the automatic, substantially continuous measurement of theparticle size substantially simultaneously with the discharge ofmaterial from the classifier. This feature together with the accurateand simultaneous control of all the vanes 30 achieved with theabove-described drive system permits almost instantaneous adjustment ofthe classifier upon the occurrence of a sensed change in particle sizein the discharge. The sampling and testing device 24 is illustrated inFIGURES l and 5-9 and, as previously noted, includes a known radiationdetector, available commercially, which is employed in a heretoforeunknown manner to measure the particle size of dry comminuted solids.

The essential parts of the measuring instrument are a source 98 ofpenetrating radiation, such as a small mass of the radioisotopecesium-l37 which emits gamma rays, and a radiation detector 100 such asan ionization cham- Iber. The instrument is conventionally manufacturedin the form of two assemblies 102, 104, one containing the source andthe other containing the detector, which are adapted to be clamped to'opposite sides of a pipe, such as a sampling tube 106, so thatradiation passes through g the tube 106 to the detector 100. Theinstrument operates by emitting an electrical signal, transmittedthrough an output cable 108, which is proportional to the magnitude ofradiation striking the detector 100. Since the magnitude of theradiation reaching the detector 100 depends on the radiation absorptioncharacteristics of the material in the tube, changes in these absorptioncharacteristics produce corresponding changes in the electrical outputsignal of the instrument.

In conventional practice the instrument is employed broadly to measurechanges in the density of a pumped liquid or liquid-solid mixture inwhich the components of the liquid or mixture differ in individualspecific gravities. More specifically, the instrument is firststandardized and calibrated for the particular material flowing throughthe pipe. These procedures are prescribed by the manufacturer of theinstrument and need not be considered here in detail. Briefly,calibration involves correlating the output signal of the instrumentwith the actual density of the pumped product as measured by some othermeans. Conventionally this is done by periodically taking samples of thematerial in the pipe, measuring the density of the samples by a standardprocedure and plotting on a graph the density of the sample against theoutput signal. During subsequent operation with the same product theoutput signal may be read directly in units which are related to thedensity of the measured solution or slurry. For example, the signal maybe calibrated in terms of actual density, specific gravity, degrees Baumor percent solids (in the case of a slurry).

In the case of a mass of dry pulverized solids moving through a pipethere will normally be inherent variations in the compaction of thepowder as it tumbles along. While the compaction will depend in part onthe particle size of the powder, the normal forces of gravity and themechanical agitation causing the movement will produce random variationsin compaction and thus random variations in the density of the material.The application of a radiation-type density instrument to such a pipewill give a signal which varies with the total density changes, but thesignal will not be an accurate measure of the particle size. Accordingto the principles of the present invention, the output signal is maderesponsive only to particle size by assuring that the compactionproduced by other means is uniform throughout the mass being tested andremains constant as the mass passes by the detector. When this is donethe density variations, after proper calibration of the instrument forthe particular material being tested, will be a measure of the particlesize. The signal transmitted by the output cable 108 may be employed tocontrol the vane drive motor 76 automatically or to produce a visualsignal for use by an operator.

Referring now to the sampling portion of the device 24 it will berecalled that it includes the previously mentioned horizontal screwconveyors 26, 28 which are associated with the iine discharge section 22of the classier 10. As seen in FIGURE 1, the upper, or sampling conveyor26, is provided with an inlet hopper 110 having an open upper endadapted to receive a portion of the solids which descend through thedischarge section 22 during operation of the classifier 10. The righthand, or discharge end of the upper conveyor 26 communicates with theadjacent end of the lower conveyor 28 by means of a short vertical chute112. The left hand, or discharge end of the lower conveyor 28communicates with the classifier discharge section 22 through adischarge opening 114 in the bottom of the conveyor housing. Inoperation the conveyors 26 and 28 may be operated at the same speed sothat a stream of solids which is withdrawn from the classifier 10 willbe returned thereto. During a testing operation, however, a smallproportion of the solids passing through the lower conveyor 28 will bewithdrawn downwardly into the sampling tube 106. The conveyor 28 mayalso be provided with sample retrieving container 115 and associatedvalve 117.

The conveyors 26 and 28 are driven by an electric motor 1116 which isshown mounted on a suitable support plate 118 above the upper conveyor26. One end of the motor output shaft drives the lower conveyor shaftthrough a belt drive 120. The upper conveyor shaft is driven from theleft end of the lower conveyor shaft through a belt connection 122 whichincludes a clutch 124 for disengaging the upper shaft.

As best shown in FIGURES 5, 6 and 7, the testing portion of deviceincludes the sampling tube 106 and a dispensing arrangement foruniformly delivering a small proportion of solids from the lowerconveyor to the upper end of the tube 106. In the illustrated embodimentthe dispensing arrangement includes a longitudinal section of thehousing of the lower conveyor, this section being in the form of asleeve 126, provided with a longitudinal slot 128 through which solidsmay pass by gravity and by the action of the screw so as to drop intothe tube 106. The latter is provided with a plunger 130 which is movedslowly downwardly during a testing operation, the rate of movement ofthe plunger 130 and the size of the slot 128 being so related that theentering solids form a uniformly loosely compacted column within thetube 106 above the plunger 130. In the illustrated embodiment it isdesired to discharge the column of solids back into the lower conveyor28 after the testing operation. In order to accomplish this, the slottedhousing sleeve 126 is mounted for 180 of rotation and is provided `witha large discharge aperture 132 diametrically opposite the slot 128.

The sampling tube 106 may have a diameter of, for example, 12 inches andconveniently is constructed of transparent material such as Pyrex glass.As seen in FIG- URES and 6 the upper end of the sampling tube 106 isdisposed within a support frame 129 and is seated and sealed therein bya gasket 131. As best seen in FIGURE 9 the lower end of the samplingtube 106 rests on a support spider which consists of a hub and threearms 133 each terminating at its outer end in an upwardly extendinglinger 134. The hub is supported from below by the upper end of athreaded stud 135 which is carried by a rigid frame member 136.

Referring more specifically to the dispensing sleeve 126, it will beseen that in the illustrated embodiment, the mounting includes a ringgear 138 attached concentrically to each end of the sleeve 126, eachring gear 138 being supported by upper and lower spur gears 140. Thelatter are keyed to axles 142 which are journalled in the supportingcasing 129. The axles 142 extend beyond the casing and terminate insuitable ttings which may be gripped for rotation by hand tools or by amotor connection. As seen in FIGURES 5 and 6 there is provided withinthe supporting casing 129 a fixed semicylindrical shroud 146 disposedabove the dispensing sleeve 1216 and in engagement therewith so as toclose the discharge opening 132 when the sleeve 126 is in the samplingposition. Similarly, the shroud 146 will close the sampling slot 128when the sleeve 126 has been rotated 180 from the position shown in thedrawings. Conveniently the shroud 146 is supported by a pair ofstationary wings 144 suspended from the upper axles 142.

FIGURE 8 illustrates the details of a preferred form of plunger 130 forsupporting the column of pulverized solids in the tube 106. As shown,the plunger 130 includes a pair of thin-walled, truncated cone-likesteel blades 148, 150 which are disposed coaxially in the tube 106 withtheir smaller ends facing downwardly and with a thick-walled rubbermember 152, of similar configuration clamped between them. The clampingmeans includes upper and lower horizontal discs 154, 156 which are drawntoward each other by a suitable connection, such as an exteriorlythreaded nipple 158, a pair of nuts 160 and a spacing disc 162. Thelower end of the nipple 158 is shown capped but may be connected to asource of air pressure when it is desired to air blend the sample in thetube 106. The lower ends of the blades 148, 150 abut an upwardly andoutwardly facing frusto-conical surface 164 on the lower disc 156, andthe upper ends are ground t0 sharp edges 166 which engage the wall ofthe tube 106. The lower portions of the blades 148, 150 are engaged byoppositely facing frusto-concal surfaces 168, 170 on the discs andforced tightly against the rubber member 152. The portion of each blade148, 150 which extends beyond the discs is slotted at a plurality ofcircumferentially spaced locations 172 so as to define a plurality ofsegments 174. The material of the blades 148, 150 is sufficiently thin,for example 1g-inch, that the segments 174 are exed inwardly withoutbreaking when the plunger 75 is forced into the tube 106. Duringmovement of the plunger 130 the segments 174 are biased outwardly bytheir own resiliency into tight contact with the wall of the tube 106.The resiliency and exibility of the segments 174 are important also ineliminating chattering which would tend to compact powder in the tube106 in a non-uniform manner.

Ordinarily pulverized powder will not follow the plunger 130 smoothly asit moves downwardly because the friction of the powder particles withthemselves and with the wall of the tube 106 causes uneven packing andarching of the powder. To offset these effects, there is provided a pairof chains 176 connected to the plunger 130 and embedded in the powderedmaterial. Conveniently, the chains 176 are also employed as part of thedrive for the plunger 130. As shown, the chains 176 are disposed asvertical loops supported at their upper ends by a pair of sprocketwheels 178 mounted on the upper support plate 118 and at their lowerends by another pair of sprocket wheels 180 carried by the frame member136. One run of each loop is disposed inside the tube 106 where it isconnected to the upper and lower clamping discs 148 and 150 of theplunger 130. The other runs lie outside the tube 106 where theyconveniently ride in vertical tubular members 182. Tension in the chains176 is adjusted by rotating the stud 135 so as to move the frame member136 up or down. Proper alignment of the frame member 136 during thismovement is obtained by two sleeves 183 xed to the member 136 andslidably engaging the lower end of the tubular members 182.

The driving mechanism for the chains 176 may take any suitable form. Asshown, there is provided a variable low speed gear motor 184 mounted onthe upper support plate 118 with its output shaft coaxial with the shaftof the conveyor drive motor 116 The output shafts of both motors aredrivingly connected to both upper sprocket wheels 178 through a pair ofclutches 186, 188 and a gear reducer 190. Both clutches 186, 188 arecontrolled by a manual lever 192 arrangement which engages one clutchwhile disengaging the other. When the left hand clutch 186 is engaged,the chains 176 will be driven by the low speed motor 184 in a directionto move the plunger 130 downwardly at a low speed, for example, 5-20inches per hour. When the right hand clutch 188 is engaged, the chains176 will be driven by the high speed motor 116 in the opposite directionat a much higher rate, for example, 30 inches per minute. Limit switches194 and 196 may be provided near the bottom and top of the tubularmember 182 to prevent over travel of the chains 176.

Operation The actual movement of the vane control rods 34 by thetransmissions 32 requires no detailed description. It is apparent thatrotational movement of the flexible drive shafts 82 and 84 impartrotational movement to each drive sprocket 44 with the result that theupper and lower runs of the chains 40 move in linear directions alongradii of the classifier 10. The control rods 34, being secured to theupper runs of the chains 40, are moved inwardly or outwardly relative tothe vertical axis of the classifier 10 in accordance with movement ofthe chains 40. The range of movement is limited by operation of thelimit switches 92 which will stop the vane drive motor 76 atpredetermined in and out positons of the control rods 34 in the eventthat the equipment should malfunction and over-run.

The construction and arrangement of the control rods 34 and theirsupporting members 54 are designed to minimize dust collection and to beself-cleaning of dust which does accumulate. When the rods 34 aredisposed in their full out positons, their bearing surfaces are fullyprotected from dust by being encased within the channel shapedsupporting members 54. In any of the inner positions, part of thebearing surfaces of the rods 34 are eX- -posed to the dusty atmospherein the classifier and will collect dust, However, the provision of thelongitudinal ribs 65 on the rods 34 aids in loosening accumulated dustwhen the latter 34 are moved outwardly.

The drive motor 76 for the vanes may be under the control of an operatoror it may be controlled automatically with a servo-mechanism inaccordance with a signal generated, for example, by the instrument 102,104. In either case the vane motor 76 is driven in one direction or theother depending on whether it is desired to increase or decrease thesize of the particles being discharged through the inner cone of theclassier 10. One of the important features of the arrangement is thesimplicity and economy of the manner in which uniform and simultaneouspower is transmitted to the drive sprockets 44 of the transmissions 32and then to the chains 40. This is effected primarily by the use of thesingle motor 76 in combination with the plurality of flexible shafts 82,84 connecting the transmissions 32. This combination eliminates the needfor a separate power source for each vane 30 and at the same time doesnot require a complicated or expensive drive linkage between the singlepower source 76 and the transmissions 32. The flexible shafts 82, 84 aresimply installed and, by virtue of their exible nature, they eliminatethe need for the more expensive mechanical components generally employedfor transmitting rotary power along a curved path. The shafts 82, 84require no lubrication along their lengths or at the points ofconnection to the transmission drive shafts and thereby require nomaintenance.

Further, the flexible shafts 82, 84 provide positive uniform transmittalof power by virtue of their low internal friction and their lack ofdistortion under load. That is, the shafts transmit rotary power withoutany differential movement or time lag between the power input shaft andthe driven shaft. Thus, if a vane control rod 34 tends to bind, theforce necessary to free the rod 34 is automatically transmitted to thatrod without any disturbance of the synchronous movement of all the rods.The arrangement therefore assures snychronous movement of the vanes 30by means of a simple and maintenance-free drive system- It would bepossible, of course, to provide each rod with a separate electric orhydraulic motor, but synchronization of such systems would requiresensitive electrical or hydraulic controls.

It will be understood that the above-described advantages of simplicity,economy and accuracy may be achieved even if more than one vane drivemotor 76 is employed so long as each motor 76 is drivingly connected toa plurality of transmissions 32.

IThe sampling and testing device 24 operates continuously during a test,the length of the test being determined by the length of the sample tube106 and the speed at which the plunger l130 moves downwardly. Samplingperiods of from 8 to l.4 hours are suitable yfor most installations.'During this time, a portion of the pulverized solids passing downwardlythrough the iine discharge section 22 will continuously collect in thehopper 110 and be carried to the right by the upper conveyor 26. Thematerial will drop through the chute 112 and then be returned to thedischarge section 22 by the lower conveyor 28. Generally the capacity ofthe conveyors 26, 28 will -be about 50 percent of the mass oW rate intothe discharge section 22 so that the material in the conveyors willconstitute a representative sample of the main product stream.

When it is desired to run a particle size test, the plunger 130 is moveddownwardly at a slow constant rate while a portion of the solids in thelower conveyor 28 is allowed to drop through the slot 128 in the sleeve126 and into the sampling tube 106. The material will have beenthoroughly mixed :by the screw in the upper conveyor 26 so that therelatively small sample which is deposited Ain the tube '106 isrepresentative of the main product stream. Downward movement of theplunger is obtained by operation of the low speed motor 184 operatingthrough the clutch 1,86, the speed reducer and the sprockets 178, aplunger speed of 5 to 20 inches per hour being suitable for mostinstallations. The width of the slot 128 is so related to thepour-ability of the powdered solids and to the speed of the plunger 130that solids pass Iinto the tube 106 at a rate equal to the rate ofdescent of the plunger 130 with the result that solids in the upper partof the tube 106 are uniformly loosely packed. In addition, the size andshape of the slot 12'8 is designed so that screw conveyor forces willnot create variations in compaction due to distrubance of the sample inthe upper part of the tube 106.

The action of the chains 176 also contributes to the formation of auniformly loosely compacted mass of powder by urginng the powderdownwardly at the same rate as the plunger 130. This prevents arching ofthe material and the consequent formation of pockets and zones of higherdensity. Ordinarily powder will not ifll a tube evenly because thefriction between the particles and the wall of the tube will prevent thematerial from following the plunger smoothly. The chains 176, however,overcome this friction by straddling the powder and urging it in unisonwith the plunger yet without disturbances which would pr-oducevariations in compaction. The radiation beam from the source `98 passesbetween the inner runs of the chains 176 so that the latter do notaffect the operation of the measuring instrument, 102, 104.

The operation of the measuring instrument 102, 104 to produce a signalwhich is a measure .of the particle size has been described previously.The successful use of the instrument to measure the particle size of drypowdered solids requires that the solids pass the instrument at aconstant rate in a uniform state of compaction, and this is achieved bythe coaction of the abovediscussed dispensing arrangement 126, 128 withthe plunger 130 and the chains 176. Under these conditions the densityof the material passing downwardly in the tube 106 is constant for agiven material having a given particle size. A change in particle sizeproduces -a change in density, and since the particle size is the onlyvariable, the density change is a measure of a change in particle size.Preferably, the test is made ljust after the solids enter the top of thetube 106 so that lvariations in compaction near the plunger as thecolumn -increases in height will not alter the measurement. When theinstrument 102, 10'4 has been calibrated for the particular materialbeing processed under constant operating conditions, the output signalfrom the detect-or portion 104 may be employed in any suitable manner aslby plotting o-n a strip chart recorder for the benefit of the milloperator. The signal may also be fed to a servo-mechanism forcontrolling the vane motor 76 or to the control system for other typesof classifiers such as those which are controlled by varying the speedof an internal fan.

It will be understood, of course, that the measurement of particle sizein the described manner is not limited to its application to the outputof a classifier and may be applied to an operation in which drycomm'inuted solids are handled.

The sample is also subject to visual inspection inasmuch as the tube 106is transparent. Changes in the product may be observed as changes incolor in different levels of the sample. Since the sampling technique isclosely controlled, it is a relatively simple matter to relate the colorchanges to variables in the operation of the grinding and classifyingequipment.

When the plunger 130 reaches the bottom of the tube 106 Iit isnecessary, of course, to empty the solids from the tube and to returnthe plunger to the top of the tube. In the illustrated embodiment, theapparatus is adapted to discharge the solids back into the lowerconveyor 28 by moving the plunger 130 upwardly. This is accomplished inpart -by rotating the slotted sleeve 12-6 one-half revolution so as todispose the large -aperture 132 Iin a position adjacent the top of thetube 106. 'Rotation may be effected manually by rotating one of theaxles 142 which cooperates with the sleeve 126 through the spur gears140 and ring gears 138. The movement of the plunger 130 is then reversedat a relatively fast rate so as to force the column of solids throughthe aperture 132 into the lower conveyor 2-8 where they will lbe engagedby the screw and carried back to the classifierdischarge section 22. Ifdesired, the sample may be retrieved by opening the valve 117 andcollecting the material in the container 115. To prevent 'interferencewith solids already being transported by the lower conveyor 28, theupper conveyor 26 is shut od by disengaging the clutch 124 at the lefthand end of the conveyors.

Movement of the plunger 130 at a relatively fast rate, for example,thirty inches per minute, is conveniently obtained by `driving thesprockets 178 and chains 176 with the high speed conveyor motor 116.This is effected in the illustrated embodiment by manually shifting thelever 192 in a direction to disengage the clutch 186 and engage theclutch 188, the latter effecting a driving connection between the leftend of the shaft of the motor 116 and the sprockets 178. When theplunger 130 reaches a point near the top of the tube, the lever 192 ismanually shifted to reverse the clutches 186 and 188 so that the lowspeed motor 184 will operate the plunger 130 during the next test. Theslotted sleeve 126 is also rotated manually to dispose the slot 128 in aposition adjacent the end of the tube 106. In this position of thesleeve 126 the discharge aperture 132 is closed by the semi-cylindricalshroud 146.

The purging action of the plunger 130 is facilitated by the chains 176which prevent packing of the powder and the creation of radial forceswhich might break the tube 106. The straddling of the powder by themoving chains 176 distributes the moving forces along the length of thecolumn of material and overcomes the frictional forces which tend toconcentrate at the wall of the tube 106. In the absence of some meansfor reducing the wall friction, many types of powder would pack sotightly that jamming of the plunger 130 or bursting of the tube 106, orboth, might occur. The ability of the plunger to flex and the sharpenededges 166 of the segments 174 assure that the wall of the tube 106 willbe cleaned of all traces of powder.

It will be appreciated that the above-described purging operationrenders the tube and plunger combination useful as a metering device forconveying dry powdered solid's at closely controlled rates. This part ofthe invention may therefore be employed, for exmple, as a dispenser forcontinuously adding one powder to a process stream of another materialwhich may be gas, liquid, slurry or another powder.

The various features of the invention are particularly applicable to acontinuous grinding operation where it is necessary to obtain a closelygraded product. In the manufacture of cement, for example, the economicsof the process and the properties of the ground clinker which is theultimate product, are closely related to particle size. The presence ofunder-sized and over-sized particles in a batch adversely affects theentire batchY so that blending of Various batches is often resorted toin order to obtain a satisfactory product. In addition, under-sizedparticles represent higher manufacturing costs' because of theover-grinding which has occurred. As previusly pointed out, priormethods of controlling the particle size either by adjusting thegrinding machinery or the classifier, or both, have depended on theperiodic taking of samples and the subsequent analysis of each samplefollowed by adjustment of the process equipment. These sequentialprocedures do not provide continuous and accurate control over theprocess with the result that relatively large changes occur in theparticle size of the product stream.

The present invention, on the other hand, provides continuous automaticmeasurement of particle size almost instantaneously with the passing ofthe product stream from the process. The process variables may thereforebe adjusted almost as soon as a product change is sensed. In the case ofa classifier of the type controlled with radially adjustable vanes, theinvention provides a further advantage in effecting simultaneousaccurate movement of all the vanes.

The details of the illustrated embodiment of the invention are given byway of example and are not intended to be limiting except as they appearin the appended claims.

What is claimed is:

1. In a particle size air classifier of the type having inner and outercones for the discharge of coarse and fine particles, respectively, agenerally cylindrical casing above said cones and a plurality ofadjustable control members disposed within said casing incircumferentially spaced apart relationship for controlling the aircurrents in said classifier in a manner to adjust the classifying actionof said classifier: a drive subassembly associated with each controlmember for moving the latter between predetermined -control positions,said subassemblies being mounted on said casing in arcuately spacedapart relationship, each of said subassemblies including a rotary inputshaft and a transmission driven by said input shaft for convertingrotary motion to the desired movement of its respective control element;and drive means for delivering rotary motion simultaneously to aplurality of said subassemblies, said drive means including a motorhaving a rotary output shaft, a driving connection between said motorand at least one of said transmission input shafts `and a plurality ofrotary drive shafts, said drive shafts connecting said one transmissioninput shaft in sequence with the input shafts of a plurality of othertransmissions.

2. Apparatus as in claim 1 wherein said drive shafts are flexible driveshafts constructed of a central straight wire core and a plurality oflayers of wrapped wire surrounding said core.

3. Apparatus as in claim 2 wherein each of said transmission inputshafts is generally tangent to a circle passing through all saidtransmissions and wherein said flexible shafts connect said input shaftsend-to-end.

4. Apparatus as in claim 1 wherein said transmission includes inner andouter sprockets horizontally spaced apart along a radius of saidgenerally cylindrical casing, said outer sprocket forming part of thedriving connection between said transmission and said drive shaft, achain looped over said sprockets, an elongated horizontal support membercarrying at one end, one of said control members; means connecting saidchain to said control member near its other end 4whereby rotation ofsaid outer sprocket moves said support member longitudinally of itself;a fixed generally tubular member surrounding at least a portion of saidsupport member and cooperating therewith to remove accumulated dust fromsaid support member upon longitudinal movement of the latter.

5. Apparatus as in claim 4 wherein said generally tubular member is anelongated horizontal member having a longitudinal slot in its lowersurface, said connecting means riding in said slot.

References Cited UNITED STATES PATENTS 2,148,452 2/ 1939 Fraser.2,243,859 6/ 1941 Fraser. 2,312,730 3/1943 Ring 222-365 2,361,1663 `10/1944 Stine 222-365 X 2,807,523 9/ 1957 Wood. 2,973,861 3/ 1961 Jager209-1 i3,128,786 4/ 1964 Badgett. 3,244,325 4/1966 Lindquist 222-371 X3,328,587 l6/ 1967 Brown et al.

FOREIGN PATENTS 972,056 10/1964 `Great Britain.

TIM R. MILES, Primary Examiner.

U.S. Cl. X.R.

